Battery separator for a storage battery

ABSTRACT

A battery separator for a lead acid (storage) battery is made from a thermoplastic sheet material. The sheet material has a central region flanked by peripheral regions. The central region includes a plurality of longitudinally extending ribs that are integrally formed from the sheet material. The peripheral regions are free of ribs and may include a densified structure. Also disclosed are a method of producing the foregoing separator, an envelope separator made from the sheet material, and a method of making the envelope separator.

RELATED APPLICATIONS

This divisional application claims the benefit of earlier-filed,co-pending U.S. Provisional Application No. 61/174,030, filed Apr. 30,2009, U.S. patent application Ser. No. 12/768,821 filed Apr. 28, 2010,now U.S. Pat. No. 8,404,378, and U.S. patent application Ser. No.13/772,445 filed Feb. 21, 2013, now U.S. Pat. No. ______, each of whichis incorporated herein by reference in their entirety.

FIELD OF THE INVENTION

The invention relates to a battery separator for a storage battery, to amethod for its production, to an envelope separator, and to a method forthe production of an envelope separator.

BACKGROUND OF THE INVENTION

Separators currently used in lead acid (or storage) batteries aremicroporous films of sheet material that prevent shorting betweenneighbouring electrode plates of opposite polarities and plate materialfrom falling out, but on account of their porous structure permit ioniccurrent flow in the electrolyte. Separators of this kind are known from,for example, U.S. Pat. Nos. 3,351,495, 4,927,722, 5,776,630 and WO 01/13442 each is incorporated herein by reference. Typical polymers theseseparators are made from include polyolefins such as high molecularweight polyethylene (e.g., ultra high molecular weight polyethylene,UHMWPE). Such separators are normally provided on at least one side withlongitudinal ribs that are intended to prevent direct contact of thesheet material with the positive electrode plate and maintain thespacing between the opposing electrodes. These ribs also lend theseparator a certain rigidity in the longitudinal direction. Longitudinalribs of this kind may also, as described in U.S. Pat. No. 5,679,479 andU.S. Pat. No. 5,789,103 both incorporated herein by reference, consistof a plurality of individual stamped embossments that form a ribstructure of alternating ridges and furrows.

Separators are usually manufactured by extrusion of a thermoplastic intoa film that is then rolled into a sheet material with the prescribedribs, after which the pore former, such as mineral oil, is extracted andthe sheet material so formed is wound into rolls. This sheet material islater drawn off the roll and cut into strips of the desired width. Thesestrips are cut to the desired length and then folded over either apositive or a negative electrode plate to form an envelope, the twoperipheral regions of which can be joined by, for example, heat sealing,pressure welding or other processes that are known per se. Electrodeplates are then assembled into groups for a storage battery, plates inseparator envelopes alternating with plates of opposite polarity withoutenvelopes. In general, only electrode plates of a single polarity areplaced in envelope separators; in special cases, however, electrodeplates of both polarities can be placed in envelope separators. Theelectrode plates within a group are now aligned and then joinedtogether. The alignment of the electrode plates may result in individualelectrode plates being pushed to a greater or lesser extent into one orthe other peripheral region of an envelope separator. Because theelectrode plates frequently acquire pointed tips or sharp edgesdepending on the manufacturing process, this displacement can cause apoint or edge of an electrode plate to puncture the separator material,which in turn can result in shorting with the neighbouring electrode.This is especially the case when the electrode plates used consist of agrid of, for example, expanded or stamped metal into which the actualactive material is incorporated, as described for example in EP-A-0 994518. In such cases it may occur that the expanded material is not cutprecisely at the nodes, so that individual grid wires project from theelectrode plates, bend slightly on alignment of the electrode plates andpuncture the sheet material of the separator.

To avoid, or at least reduce, the risk of puncture by the points, edgesor grid wires of the electrode plates, it has been proposed that theperipheral region be designed as a plurality of parallel, concavefurrows interspersing a plurality of similarly formed small “mini-ribs”(EP-A-0 899 801, JP 2000-182593, U.S. Pat. No. 6,410,183 each isincorporated herein by reference) and that the ribs between the furrowsbe broader and with a flat upper surface (WO 00/63983 incorporatedherein by reference). It has been shown, however, that in unfavourablecases it is still possible for individual envelope separators to bepunctured during alignment of the electrode plates, with the associatedrisk of shorting. It has also been proposed to design the mini-ribs inthe form of a triangle projecting from the level of the sheet material,with the base of the triangle on the sheet material, one side of thetriangle facing the inner region and the other side facing theperiphery, the side facing the inner region being longer than thatfacing the periphery.

However, it has been found for the prior art separators that manypunctures still occur in the peripheral region with separators havingmini-rib configurations.

SUMMARY OF THE INVENTION

In accordance with at least selected embodiments, a battery separatorfor a lead acid (storage) battery is made from a thermoplastic sheetmaterial. The sheet material has a central region flanked by peripheralregions. The central region includes a plurality of longitudinallyextending ribs that are integrally formed from the sheet material. Theperipheral regions are preferably free of ribs and may include adensified structure. Also disclosed are a method of producing theforegoing separator, an envelope separator made from the sheet material,and a method of making and using the envelope separator.

It is therefore at least one object of at least one embodiment of thepresent invention to provide an improved battery separator for a storagebattery so as to further reduce the risk of the electrode platespuncturing the sheet material of the separator, and to provide anefficient method for producing such separators.

It is a further object of at least one embodiment of the presentinvention to provide an improved envelope separator for an electrodeplate of a storage battery as well as a method for its production.

It is yet another object of at least one embodiment of the presentinvention to provide an improved battery separator, an improved methodfor producing such separators, or an improved method for using suchseparators.

DESCRIPTION OF THE DRAWINGS

The present invention may be better understood when considering thefollowing description of the invention along with the following drawingswhich illustrate selected exemplary embodiments of the invention.

FIG. 1 is a plan view of a battery separator made according to at leastone embodiment of the present invention.

FIG. 2 is a sectional view of the separator shown in

FIG. 1 taken along sectional line 2-2.

FIG. 3 is a schematic illustration of a process for producing theseparator shown in FIG. 1.

FIG. 4 is a sectional view of the calendaring step illustrated in FIG. 3and is taken along sectional line 4-4.

FIG. 5 is a perspective view of a ‘universal profile.’

FIG. 6 is a perspective view of a ‘panel profile.’

FIG. 7 is a schematic illustration of a process for producing anenvelope separator.

FIG. 8 is a plan view of at least one embodiment of an envelopeseparator.

FIG. 9 is a plan view of the sheet material of at least one embodimentof the present invention with lateral edges folded over.

FIG. 10 is a schematic illustration of a process for producing thematerial shown in FIG. 9.

DESCRIPTION OF THE INVENTION

In accordance with at least one embodiment of the present invention, andas shown in FIGS. 1 and 2, a battery separator 10 for a storage battery,preferably said separator being made of a sheet material 52 being basedon a thermoplastic polymer, whereby said battery separator has alongitudinal direction 12 and a width direction 14 and has a centralregion 16 and in the width direction at its side edges peripheralregions 18 extending in the longitudinal direction. The batteryseparator 10 has longitudinal main ribs 20 extending in the longitudinaldirection and being formed integrally with the sheet material 52 (orback sheet or web) on at least one side of the sheet material 52, themain ribs 20 having a distance 22 with respect to each other, wherein atleast the sheet material 52 of the battery separator in its centralregion 16 has a microporous structure having an average porosity, andwherein the peripheral regions 18 are essentially free from main ribs20.

In a preferred embodiment, the peripheral regions 18 of the batteryseparator 10 according to at least selected embodiments of the inventionhave a densified structure 24 the porosity of which is lower than theporosity of the microporous structure in the central region 16.Especially preferred is a densified structure 24 in the peripheralregions 18 with an average porosity which is at least 10% by volumelower than the average porosity in the central region 16 of the sheetmaterial 52.

It has been shown that for such battery separators 10 having peripheralregions 18 which are essentially free from main ribs 20 puncture of thesheet material 52 by any electrode material can effectively be reduced.It is assumed that this is due to the fact that in the peripheralregions 18 of the separators 10 of the invention there are essentiallyno catch points for the edges of electrode plate or for sharp gridwireends of expanded metal grids the electrodes are made from as is stillthe case e.g. with separators having a mini-rib configuration in theperipheral areas. In addition, the densified structure 24 and thereduced porosity in the peripheral regions 18 may lead to an improvementwith respect to puncture resistance. Within the framework of the presentinvention, essentially free from ribs 20 shall mean that there are noribs 20 in the peripheral regions 18 of the separators 10 according tothe invention like the major ribs 20 in the central region 16 of theseparator 10, which typically have a height above the sheet materialbetween the ribs 20 of about 0.3 mm to about 2.0 mm, and no pattern ofmini-ribs like the ones of the separators described in the prior art.However, embodiments of the peripheral regions 18 are comprised by thepresent invention whose surfaces show singular surface protuberanceswhich have a height below 0.05 mm.

In accordance with at least selected embodiments, the invention alsorelates to a method 50 for producing such a battery separator 10 (FIG.3), in at least one embodiment, the method comprising the steps:

a) providing a sheet material 52 being made of a thermoplastic polymerand having a longitudinal direction 12 and a width direction and sideedges parallel to the longitudinal direction, said sheet material 52having longitudinal main ribs 20 extending in the longitudinal directionand being formed integrally with the sheet material 52 on at least oneside of the sheet material 52, whereby the main ribs 20 have a distance22 with respect to each other and whereby the sheet material 52 has amicroporous structure having a porosity,

b) feeding the sheet material 52 in longitudinal direction 12 into acompression device 54, and

c) compressing the sheet material 52 by applying a compressive forceuniformly in a peripheral region 18 along each side edge but not in acentral region 16 between the peripheral regions 18 to provide a surfaceof the sheet material 52 in the peripheral regions 18 being essentiallyfree from ribs 20.

With reference to FIG. 4, compressing of the sheet material 52 in theperipheral regions 18 can be done in a calendering process step 56between pressure rollers 58, 60. Preferably, by the compressing of thesheet material 52 in the peripheral regions 18 in the methods of theinvention, the structure in the peripheral regions 18 is densified andthe porosity is lowered compared to the average porosity of themicroporous structure of the uncompressed sheet material 52 in thecentral region 16 between the peripheral regions 18. It is especiallypreferred if compressing is done such that in the peripheral regions 18the densified structure 24 has an average porosity which is at least 10%by volume lower than the average porosity in the central region 16 ofthe sheet material 52.

Typically, the distance 22 (FIG. 1) of the main ribs 20 in the centralregion 16 of the sheet material 52 varies between about 5 mm and 12 mm.In a preferred embodiment, the width of each peripheral region 18 of thebattery separators 10 of the present invention or the peripheral regions18 resulting in the processes according to the present invention is atleast by a factor of 1.5 larger than the average distance betweenadjacent main ribs 20.

Preferably, the sheet material 52 used within the framework of at leastone embodiment the present invention has a thickness 64 (FIG. 2) ofabout 0.05 to 0.35 mm between the main ribs 20. As a result of thecompression, the thickness of the sheet material 52 in the peripheralregions 18 may be slightly thinner or similar depending amongst otherthings on the mass of the ribs 20 which are removed (flattened) by thecompression.

There is no restriction with respect to the pattern of the main ribs 20extending in the longitudinal direction of the sheet material 52. Thesheet material 52 may also have transverse ribs, not shown, like e.g.disclosed in U.S. Pat. No. 5,776,630 (on the same side as main ribs 20)or as in U.S. patent application 61/253,096 (on the back side of sheet52), each hereby incorporated by reference herein. In addition to themain ribs 20, the sheet material 52 provided in step a) of the processof the present invention may have mini-ribs in areas along its sideedges 18.

However, in an least selected embodiments, preferably a sheet material52 is provided in process step a) the main ribs 20 of which all have thesame cross section, are equally spaced with respect to each other andare distributed across the entire width 14 of the sheet material 52(FIG. 5). In step c) in the peripheral regions 18 the main ribs 20 areremoved by the compressing of the sheet material 52 whereby a smoothsurface is formed in the peripheral regions 18 which are thenessentially free from ribs 20 (FIGS. 1 and 2). However, it may happenthat during compression step c) ribs 20 initially being present inperipheral regions 18 are not fully removed but small surfaceprotuberances remain in the peripheral regions 18. However, as mentionedabove, embodiments of the peripheral regions 18 are comprised by thepresent invention and are understood to be essentially free from ribs 20and whose surfaces show singular surface protuberances which have aheight below 0.05 mm.

Accordingly, a battery separator 10 is preferred the main ribs 20 ofwhich in the central region 16 all have the same cross section, wherebyit is especially preferred that the main ribs 20 are equally spaced 22with respect to each other.

Sheet materials 70 (FIG. 5) having a profile with longitudinal main ribs20 all having the same cross section, being distributed across theentire width direction 14 of the sheet material 70 and being equallyspaced with respect to each other, also known as “universal profile,”from an economical point of view with respect to the productionprocesses offer advantages over sheet materials 80 (FIG. 6), havinglongitudinal main ribs 20 in their central region 82 and mini-ribs 86 intheir peripheral regions 84, also known as “panel profiles.” Because ofthe mini-rib 86 areas in the peripheral region 84 panel profiles have tobe extruded and manufactured in specific width according to customerrequirements. This affords frequent changes in the production processes.In contrast, universal profiles 70 can efficiently be produced ingreater widths and sheet materials in widths specified by the customerscan be cut from the wide universal profile 70 sheet.

However, it has been proven difficult to produce envelope batteryseparators for an electrode plate of a storage battery from universalprofiles 70 as sealing of the side edges of the envelope separators posea major problem during production. Especially when using mechanicalsealing by compressing the edges into one another between a pair ofopposed pressure rolls having gear teeth as e.g. described in U.S. Pat.No. 4,407,063 incorporated herein by reference, the longitudinal mainribs 20 in the peripheral regions 84 lead to deformations of the sideedges and rib run-off in the side areas of the envelope. In accordancewith at least selected embodiments of the present invention, sheetmaterials 52 which have been compressed in the peripheral regions 18along each side edge by applying a compressive force uniformly in theseperipheral regions 18 resulting in these regions in a surface beingessentially free from ribs 20 led to envelopes separators havingstraight sealed side edges without rib run-off.

Therefore, in addition, at least certain embodiments of the presentinvention are directed to a method 90 (FIG. 7) for producing an envelopeseparator for an electrode plate of a storage battery comprising thesteps:

a) providing a sheet material 52 being made of a thermoplastic polymerand having a longitudinal direction 12 and a width direction and sideedges parallel to the longitudinal direction, said sheet material 52having longitudinal main ribs 20 extending in the longitudinal directionand being formed integrally with the sheet material 52 on at least oneside of the sheet material 52, whereby the main ribs 20 have a distance22 with respect to each other and whereby the sheet material 52 has amicroporous structure having a porosity,

b) feeding 92 the sheet material 52 in longitudinal direction into acompression device,

c) compressing 94 the sheet material by applying a compressive forceuniformly in a peripheral region 18 along each side edge but not in acentral region 16 between the peripheral regions 18 to provide a surfaceof the sheet material 52 in the peripheral regions 18 being essentiallyfree from ribs 20,

d) cutting 96 a rectangular section of the so treated sheet materialalong a line perpendicular to the longitudinal extension of the sheetmaterial 52,

e) folding 98 the rectangular section onto itself along a central line,not shown, of the piece rectangular to the main ribs 20 to form twoequally sized superimposing halves of the rectangular section, and

f) joining and sealing 100 the overlapping side edges.

It is possible to conduct the method 90 according to the invention forproduction of an envelope separator such that e.g. the sheet materialafter compressing 94 the peripheral regions may be rolled up on a roll,not shown, as an intermediate product which later on is fed into anenveloping machine for cutting 96, folding 98, and finishing 100 theenvelope. It is, however, preferred to integrate the process steps ofthe method in a single process.

Moreover, at least selected embodiments of the invention relate to anenvelope separator 110 (FIG. 8) for an electrode plate of a storagebattery, said envelope separator 110 having closed bottom 112, left 114and right 116 side edges and an open top side 118, the envelopeseparator 110 comprising a battery separator being made of a sheetmaterial 52 being based on a thermoplastic polymer, whereby the batteryseparator has a longitudinal direction, a central region 16 and twoperipheral regions 18 extending in the longitudinal direction at itsside edges and having longitudinal main ribs 20 extending in thelongitudinal direction being formed integrally with the sheet material52 on at least one side of the sheet material 52 and having a distance22 with respect to each other, wherein the sheet material 52 in thecentral region 16 has a microporous structure having a porosity, whereinthe battery separator is folded onto itself along a line 120perpendicular to the longitudinal main ribs 20 thereby forming theclosed bottom 112 of the envelope separator 110, wherein the overlappingside edges of the battery separator are joined and sealed 100 therebyforming the closed side edges 114, 116 of the envelope separator 110,and wherein the peripheral regions 18 between the longitudinal main ribs20 and the joined edges 100 are essentially free from ribs 20.

There are several methods for sealing 100 the side edges 114, 116 ofenvelope separators 110 like sealing by adhesives, heat sealing such asultrasonic, or mechanical sealing. For the envelope separator 110 of thepresent invention and in the method for its production, it is preferredthat the overlapping side edges 114, 116 are mechanical sealed bycompressing the edges 114, 116 into one another between a pair ofopposed pressure rollers acting as sealing wheels. For ensuringeffective compressing of the edges into one another, the pressurerollers preferably have gear teeth as e.g. described in U.S. Pat. No.4,407,063 incorporated herein by reference.

In a preferred embodiment of the invention in the peripheral regions 18of the battery separator or of the envelope separator 120 (FIG. 9) thebattery separator or the sheet material 52 is folded onto itself along afold line 122 parallel to the side edges. Folding can be done to eitherside of the battery separator or the sheet material 52 and for theenvelope separator 120, the folding can be done inwardly or outwardly.By the folding in the peripheral region 18, a folded over region 124 isformed with a thickness twice that of the unfolded material, whichresults in a further reduced risk of a perforation of these regions incontact with the edges or grid wires of the electrode plates, i.e. in afurther increased puncture resistance.

In the process 50 for producing the battery separator of the inventionand in the process 130 (FIG. 10) for producing the envelope separator120 of the invention the folding 132 may be done after the compressingstep 94, c), preferably directly after the compressing. In order toimprove the folding, in a preferred embodiment of the methods accordingto the invention the sheet material 52 in each peripheral region 18 isscored, not shown, along the fold line 122 parallel to the side edgesand is then folded onto itself along each fold line.

The folding 132 can be accomplished by methods known in the art forfolding sheet-like materials in continuous processes. It is, however,preferred to use gradually developing curved surfaces, i.e.plowshare-type folders like the ones described in U.S. Pat. No.2,540,844 incorporated herein by reference, or guide bars and creaseblades, respectively, like those disclosed in EP-A-0 721 908incorporated herein by reference.

The sheet material 52 may be stretched at least in the width direction14. Stretching in the width direction is especially advantageous incases when the battery separator or the sheet material afterwards isfolded onto itself in the peripheral regions in order to compensate forthe width reduction by the folding. Moreover, by stretching themicroporous structure of the sheet material is oriented in the widthdirection. Stretching may be done by, for example, a factor of 1.05 to1.2. Among other things, stretching the material will also have theconsequence of increasing the porosity of the bulk of the separator,which in turn will lower the ionic resistance of the separator andultimately the battery.

In principle, all acid-resistant thermoplastic polymers are suitable forthe sheet materials of the separators according _(t)o the invention.Preferred thermoplastic polymers are polyvinyl chloride, polyethyleneand polypropylene, polyethylene of high molecular weight (e.g., ultrahigh molecular weight polyethylene, UHMWPE) is particularly preferred.The sheet materials may also be manufactured with the addition ofinorganic fillers such as amorphous silicic acid with the compositionand manufacture of sheet materials of this type being known from theprior art. Representative formulations may be found in U.S. Pat. Nos.3,351,495, 5,230,843, and 7,445,735, each is incorporated herein byreference.

A battery separator for a lead acid (storage) battery is made from athermoplastic sheet material. The sheet material has a central regionflanked by peripheral regions. The central region includes a pluralityof longitudinally extending ribs that are integrally formed from thesheet material. The peripheral regions are free of ribs and may includea densified structure. Also disclosed are a method of producing theforegoing separator, an envelope separator made from the sheet material,and a method of making the envelope separator.

The present invention may be embodied in other forms without departingfrom the spirit and the essential attributes thereof, and, accordingly,reference should be made to the appended claims, rather than to theforegoing specification, as indicating the scope of the invention. Forexample, an improved battery may include a plurality of the batteryseparators or envelope separators of the present invention.

We claim:
 1. A battery separator for a lead acid battery comprising: athermoplastic sheet with a planar back web and a longitudinal centralregion between peripheral regions; a plurality of longitudinal main ribson at least one side the thermoplastic sheet, the main ribs are spacedapart and integrally formed with the thermoplastic sheet; and, aplurality of transverse ribs on at least the other side thethermoplastic sheet.
 2. The battery separator according to claim 1wherein in the central region the sheet between the main ribs has athickness of 0.05 to 0.35 mm.
 3. The battery separator according toclaim 1 wherein the sheet material is formed into an envelope.
 4. Thebattery separator according to claim 3 wherein overlapping edges of theenvelope are mechanically sealed to one another.
 5. A lead acid batterycomprising the battery separator of claim
 1. 6. A lead acid batterycomprising the battery separator of claim
 3. 7. The battery separatoraccording to claim 1 having a plurality of transverse ribs on both sidesof the thermoplastic sheet.
 8. The battery separator according to claim1 having a plurality of transverse ribs on only the other side of thethermoplastic sheet from said longitudinal main ribs.
 9. A batteryseparator for a lead acid battery comprising: a thermoplastic sheet witha planar back web and a longitudinal central region between peripheralregions; a plurality of longitudinal main ribs on at least one side thethermoplastic sheet, the main ribs are spaced apart and integrallyformed with the thermoplastic sheet; a plurality of transverse ribs onat least the other side the thermoplastic sheet, the transverse ribs areintegrally formed with the thermoplastic sheet.
 10. The batteryseparator according to claim 9 wherein the plurality of transverse ribsare only on the other side of the thermoplastic sheet from the mainribs.
 11. The battery separator according to claim 9 wherein theplurality of transverse ribs are on both sides of the thermoplasticsheet.
 12. The battery separator according to claim 9 wherein the sheetmaterial is formed into an envelope.
 13. The battery separator accordingto claim 12 wherein overlapping edges of the envelope are mechanicallysealed to one another.
 14. A lead acid battery comprising the batteryseparator of claim
 9. 15. A lead acid battery comprising the batteryseparator of claim
 12. 16. An envelope battery separator for a lead acidbattery comprising: a thermoplastic sheet with a planar back web and alongitudinal central region between peripheral regions; a plurality oflongitudinal main ribs on at least one side the thermoplastic sheet, themain ribs are spaced apart and integrally formed with the thermoplasticsheet; a plurality of transverse ribs on at least the other side of thethermoplastic sheet, the transverse ribs are integrally formed with thethermoplastic sheet; and, wherein the sheet material is formed into anenvelope.
 17. The battery separator according to claim 16 whereinoverlapping edges of the envelope are mechanically sealed to oneanother.
 18. The battery separator according to claim 16 wherein theplurality of transverse ribs are only on the other side of thethermoplastic sheet from the main ribs.
 19. The battery separatoraccording to claim 16 wherein the plurality of transverse ribs are onboth sides of the thermoplastic sheet.
 20. A lead acid batterycomprising the battery separator of claim 16.